In semiconductor processes of forming an MOS transistor, heat treatment of a wafer is generally performed in the final process in an atmosphere containing hydrogen. Due to this heat treatment, dangling bonds (uncombined hands) which exist in an interface between a substrate and a gate insulator are terminated and stabilized by hydrogen. As a result, the interface level density in the interface between the substrate and the gate insulator is reduced. In general, this process is called sintering process (or hydrogen sintering process).
In a high performance LSI of the next generation or later, it is demanded to apply materials which have not been conventionally used, to the LSI manufacturing process to form a gate electrode, an interconnect, an inter layer dielectric, a memory element and the like. Some of those materials may be degraded in characteristics remarkably due to high temperature heat treatment or a reducing atmosphere containing hydrogen in the hydrogen sintering process.
Such degradations in characteristics can be suppressed by lowering the temperature in the hydrogen sintering process. In this case, however, the diffusion rate of hydrogen molecules and the reaction rate between the hydrogen molecules and the dangling bonds also become lower. Therefore, the lowering of the temperature is not desirable in terms of the original object, i.e., the reduction of the interface level density. Therefore, a process which can reduce the interface level density in the interface between the substrate and the gate insulator while suppressing the characteristic degradation of the materials of the LSI is needed.